1. Technical Field
The present invention relates to an optical fiber sensing system that measures the physical quantity of a measurement target object with the use of an optical fiber.
2. Background Art
Recently, a method of using an optical fiber as a sensor for detecting, for example, ground deformation, the distortion or deformation of a structure, etc., has been proposed. An example of such a method is FBG (Fiber Bragg Grating).
In the FBG method, an ultraviolet laser beam is applied to a specified core region of an optical fiber for cyclic refractive index modulation in the direction of the length of the fiber. As its optical property, it exclusively reflects light in a specified spectral range in sync with the cycle, whereas light having any other wavelength is allowed to pass therethrough. The FBG method utilizes such optical property.
If external pressure is applied to the region irradiated with the ultraviolet laser beam, or if ambient temperature changes, the index of refraction changes, which causes a shift in the wavelength of light reflected by the region. It is possible to detect, for example, ground deformation, the temperature of liquid, the displacement, distortion, deformation, etc. of a structure as described above by measuring the wavelength shift of return light.
For example, a technique for detecting whether any shock was applied to a composite material or not as well as detecting the position of the composite material and measuring the size thereof with high precision by using an FBG is disclosed in Patent Document 1. A technique for measuring the distortion of a measurement target object by using an FBG is disclosed in Patent Document 2.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2008-139171    Patent Document 2: Japanese Unexamined Patent Application Publication No. 2004-309218